The present invention relates to a method of improving film quality of an insulating film and, more particularly, to a method of improving film quality of an SiO2 film, densifying the SiO2 film by reducing impurities such as hydrocarbon, etc., which are contained in the SiO2 film (insulating film) formed by the CVD (Chemical Vapor Deposition) method using a reaction gas containing TEOS (Tetraethoxysilane), and to a semiconductor device including an insulating film of the thus improved quality.
In the prior art, after an insulating film such as a SiO2 film, etc. is formed on a substrate, e.g., a silicon wafer, a heat treatment called annealing is applied to the insulating film. This heat treatment is for the purpose of improving the film quality of the insulating film and is performed by exposing the surface of the insulating film to a high temperature atmosphere containing an inert gas such as N2, etc.
It is an object of the present invention to provide a novel film quality improving method for an insulating film that is different from the heat treatment using N2 (nitrogen), and to provide a semiconductor device including an insulating film of the thus improved quality.
In the method for improving film quality of an insulating film according to the present invention, the heat treatment is performed by exposing the surface of the SiO2 film (insulating film), which is formed by the CVD (Chemical Vapor Deposition) method using a reaction gas containing TEOS (Tetraethoxysilane), to an atmosphere containing steam. According to this method, steam or OH group dissociated from the steam enters into the interior of the SiO2 film, whereby impurities such as hydrocarbon, etc., contained in the film are oxidized, desorbed and expelled from the film. At the same time, dangling bonds of Si (silicon) atoms contained in the film are replaced with SiO2 bonds by the strong oxidizing power of the steam-containing atmosphere.
It has now been found that, if the heat treatment is performed in such a manner, a SiO2 film whose film quality is close to that of a thermal oxide film can be obtained at a lower temperature than that of the heat treatment in a N2 (nitrogen) atmosphere. The reason for this may be that the desorption of the above-mentioned impurities and replacement of dangling bonds of the Si (silicon) atoms with the SiO2 bonds can be achieved at the relatively lower temperature. Therefore, since the heat treatment is performed at a lower temperature as compared with heat treatment in a N2 (nitrogen) atmosphere, failure due to the heat treatment in the high temperature atmosphere is avoided.
It has also been found that the effect of the film quality improvement reaches not only an upper layer portion of the SiO2 film but also to almost 1.0 xcexcm in depth from a surface of the film. Therefore, the film quality improvement of the SiO2 film that is formed in a deep trench, for example, can also be attained.
Further, it has been found that change in the film thickness after the heat treatment is smaller than the heat treatment in a N2 (nitrogen) atmosphere. The reason for this may be that new SiO2 is formed on the side wall portions and the bottom portions of the deep trenches of the film by thermally oxidizing Si (silicon) layers and thus shrinkage of the film can be suppressed by the amount of such newly formed SiO2. Therefore, device failure due to the shrinkage of the film can be prevented.